Five people diagnosed with Legionnaires' disease after outbreak in Melbourne CBD

Five cases of the infectious illness Legionnaires' disease have been detected in Melbourne, with health authorities investigating possible links to cooling towers in the CBD.

Victorian deputy Chief Health Officer Finn Romanes says the three men and two women affected, aged 51 to 71, had each worked or visited the CBD in the days before they became unwell.

They are recovering after being admitted to hospital for treatment.

Dr Romanes says anyone who visited Melbourne's CBD between late March and early April and who is suffering from pneumonia or flu-like symptoms should visit their GP.

The illness causes flu-like symptoms such as headache, fever, chills, muscle aches and pains, followed by respiratory problems and pneumonia over three or four days, but can be fatal if left untreated.

People at most risk are aged over 50, heavy smokers or drinkers, people with diabetes or lung disease, and those with compromised immunity.

Twenty-six people have contracted Legionnaires' disease in Victoria so far this year.